Short-term use of folic acid, a B vitamin added to food in many countries to prevent birth defects, is unlikely to significantly increase cancer risk, according to a review of results from 13 studies. Among people who took folic acid supplements daily for five years or less, 7.7 percent reported new cases of cancer, compared with 7.3 percent among those who took a placebo, according to an analysis of studies involving almost 50,000 individuals through the end of 2010. The review was published today in the Lancet medical journal.